missing cover art
There are 2 completely different C64 conversions of the game. The US version is done by Quicksilver. The European version is done by Elite. The European Version has better graphics, sound an gameplay. It also uses the upper and lower screenborder and doesn't use the whole horizontal resolution to imitate the vertical look of the arcade.
On June 30, 1988, Ikari Warriors was put on the infamous German index by the BPjS. For more information about what this means and to see a list of games sharing the same fate, take a look here: BPjS/BPjM indexed games.
Wondering why the Spectrum version was released so late, especially considering that the ST and Amiga versions were released first? So are many Spectrum enthusiasts. Famed programmer David Perry worked on a version that was due for release in late 1986 - no one knows for sure why this version was scrapped, and a different version not released for another 18 months.
The Ikari Warriors (Ralf & Clark) would later appear as playable characters in SNK's The King of Fighters game series with brand new looks and moves. Interestingly enough, on the first KOF (where teams are country-based), the Ikari Warriors represent Brazil.